518 BACTERIOLOGY. 



The whole tube, after being plugged at the bottom 

 with glass wool and at its wide open extremity with 

 cotton wool (a, Fig. 106), is placed vertically, small 

 end down, into an Erlenmeyer flask of about 100 c.c. 

 capacity and sterilized in a steam sterilizer for the 

 proper time. It is kept in the covered sterilizer until 

 it is to be used, which should be as soon as possible 

 after sterilization. 



The watery suspension or bouillon culture of the 

 organisms is now to be filtered repeatedly through the 

 glass wool into sterilized flasks until a degree of trans- 

 parency is reached which will permit the reading of 

 moderately fine print through a layer of the fluid 

 about 2 cm. thick i.e., through an ordinary test-tube 

 full of it. It can then be subjected to the action of the 

 disinfectant, and, as a rule, the results are far more 

 uniform than when no attention is paid to the exist- 

 ence of clumps. It is hardly necessary to say that in 

 the practical employment of disinfectants outside the 

 laboratory no such precautions are taken, but in labor- 

 atory work, where it is desired to determine exactly the 

 value of different substances as germicides, all the pre- 

 cautions that have been mentioned will be found essen- 

 tial to precision. 



The disinfectant value of gases and vapors is deter- 

 mined by their influence upon test-objects in closed 

 chambers. The object is to determine the proportion 

 of the gas, when mixed with air, that is required to 

 destroy the bacteria exposed to its action in a given 

 time. For this purpose the test is commonly made as 

 follows: under a sterilized bell glass of known capacity 

 the test-objects are placed. Into the chamber is then 

 admitted sufficient of a known mixture of air and the 



